Such vibratory gyroscopes are conventionally used in inertial navigation systems, as is the case, for example, for a gyroscopic compass that is adapted to supply an angle measurement relative to a reference direction which is that of the geographical North (Heading).
Asymmetrical Coriolis Vibratory Gyroscopes (CVG), for example of the Hemispherical Resonance Gyroscope (HRG) type, more generally referred to as of type I, such as those described in the document ‘Type I and Type II micromachined vibratory gyroscopes’ by Andrei M. Shkel, pages 586-593, IEEE/ION (Institute of Electrical and Electronics Engineers/Institute of Navigation', PLANS 2006, San Diego, Calif., USA), operate in open loop mode and measure an absolute rotation angle on the basis of a measurement of an angle representing the vibration geometrical position of the gyroscope relative to measuring electrodes.
Such a gyroscope can also be used in closed loop mode by controlling the vibration geometrical position by commanding precession, as described in particular in the document FR 2 755 227.
In this case, the vibration geometrical position of the gyroscope is maintained in a fixed position, and the measurement is deduced from the command input that it is necessary to apply to the gyroscope to maintain it in that fixed vibration geometrical position. This type of operation is also referred to as ‘gyrometer looping’. The values supplied by the physical measurement then no longer correspond to an angle but to a rotation speed.
Whether used in open loop mode or in closed loop mode, the measurements supplied by these vibratory gyroscopes can be affected by errors that are essentially a function of the position of the vibration relative to the measuring electrodes. These errors are therefore variable as a function of the vibration geometrical position, and have the effect of degrading the level of accuracy of the values measured in this way. There is therefore benefit in seeking to reduce these errors in order to improve the performance of this type of gyroscope.